The present invention relates to a device for generating a plurality of laser beams suitable particularly but not exclusively for use in equipment for applying laser beam treatment to a surface that is sensitive to the impact of a laser beam.
In the manufacture of printed circuits, one of the steps consists in covering the conductive layer of the printed circuit in a layer of resist material and in exposing said layer of resist through an artwork to define the shape of the conductor tracks that are to be obtained on the printed circuit. After the resist layer has been exposed, the non-exposed zones are removed, which zones correspond to portions of the conductive layer that are to be removed in turn.
Another technique for making printed circuits is becoming popular in which the resist layer is imprinted locally by the impact of a laser beam. The laser beam impact is usually under the control of scanning equipment that includes a rotary polygonal mirror associated with a shutter device for controlled interruption of the laser beam and usually constituted by an acousto-optical modulator.
Since the number of laser beam impacts required for making a printed circuit panel of large dimensions with precision is naturally itself very large, it is advantageous to be able to subdivide the surface of the printed circuit panel into a plurality of zones and to scan each of the zones simultaneously with a respective laser beam, thereby significantly reducing the length of time required for exposing the entire panel.
However, in order to be able to achieve this result, it is necessary for the energy of each laser beam to lie, in a well-defined range corresponding to the sensitivity of the material constituting the resist layer, so that the laser radiation modifies the state of the resist uniformly at all impact points.
Furthermore, the cost of acousto-optical modulators increases when they are required to control a light beam containing a wide range of wavelengths. Acousto-optical modulators are also adapted to a certain energy range, and if this energy range is exceeded then the operation of the modulator ages more rapidly.
Finally, the efficiency of modulation increases with narrowing wavelength range.
An object of the present invention is to provide a device for generating a plurality of laser beams, each laser beam comprising a limited range of wavelengths, and each laser beam containing energy lying in a relatively limited range.
To achieve this object, the invention provides a device for generating a plurality of laser beams, the device comprising:
a laser source emitting an initial beam at P wavelengths;
a wavelength splitter assembly for splitting the initial beam into N intermediate beams, where Nxe2x89xa6P, each intermediate beam containing a group of wavelengths comprising at least one wavelength; and
Nxe2x80x2 energy splitter assemblies, where Nxe2x80x2xe2x89xa6N, for splitting an intermediate beam into ni divisional beams, each of the ni divisional beams having substantially the same energy, whereby K divisional beams are obtained with   K  =      N    -          N      xe2x80x2        +                  ∑                  i          =          1                          i          =                      N            xe2x80x2                              ⁢              n        i            
It will be understood that by beginning by splitting the laser beam emitted by the source into a plurality of intermediate beams, beams are obtained at the outlet from the splitter occupying wavelength ranges that are well defined and without overlap. It will also be understood that in the second step which consists in splitting the energy of at least some of the intermediate beams, the divisional beams that are finally obtained occupy well-defined wavelength ranges and have energy that is easy to define.
Preferably, the wavelength splitter assembly comprises:
a device for splitting said initial beam into P unit beams, each unit beam corresponding to one wavelength; and
N means for grouping together some of the P unit beams in a given group of wavelengths, the wavelengths of a group being disjoint from the wavelengths of another group, thereby obtaining N intermediate beams.
By means of this step of partially recombining monochromatic laser beams, the monochromatic beams belonging to the same group are re-colinearized. They can be processed, for example, by acousto-optical modulators or more generally by optical systems with substantially the same precision as a monochromatic beam.
Another object of the invention is to provide equipment for treating a surface that is sensitive to a laser beam, in particular for treating the layer of resist formed on the metal layer of a printed circuit in order to obtain the conductor tracks of said printed circuit, or to treat the metal layer directly.
The treatment equipment comprises:
a device for generating K divisional laser beams of the above-defined type;
K acousto-optical modulators, each modulator receiving a divisional beam, each modulator being adapted to the group of wavelengths of the divisional beam it receives and being adapted to its energy; and
deflector means for deflecting each modulated laser beam so that each modulated laser beam scans a fraction of said surface.